Low density plasma experiments investigating laser propagation and proton acceleration

Transcription

1 Low density plasma experiments investigating laser propagation and proton acceleration L Willingale, K Krushelnick, A Maksimchuk Center for Ultrafast Optical Science, University of Michigan, USA W Nazarov University of St Andrews, UK PM Nilson, C Stoeckl, TC Sangster LLE, University of Rochester, USA

2 Motivation Laser propagation and channeling in near critical, densities is 3 important for the hole boring fast ignition scheme Ion acceleration at near-critical densities has been shown to be an interesting regime for producing high energy ion beams (b) 5 fs pulse a = 5 Electron density (/n c ) Initial target location Laser axis (µm) 3 nm 3 nm + nm Al 3 nm + nm Al 3 Figure 3. Axial electron density profiles (i.e. at the center of the t by the DUED simulations for a target composed of 3 nm SiO targets with the same layer plus and nm of Al on top ( being on the laser incident side). The profiles are shown at ti after the onset of a laser pedestal with constant intensity I = 5 The laser irradiates the target from the right-hand side. The targe located at. Maximum proton energy (MeV) 5 5 experiment D PIC.. Target thickness (µm) L Willingale et al, IEEE trans. Plas. Sci, 3, 5 () n e (n c ) L Willingale et al, PRL,, 5 (9). Experimental results Figure. Maximum proton energy versus target thickness us targets of different Increasing thicknesses intermediate density contrast conditions the D PIC simulations, squares the experimental values. Each exp point includes several shots (from to 3) and the error bar on ene the recorded rms shot-to-shot fluctuation. Error bars for nm smaller than the box width. Lines are guides for the eye. P Antici et al, New Journal of Physics,, 33 (9) Figure shows the maximum proton energies recorded by RCFs and the magneti in these various plasma conditions. Each data point includes several shots (fro

3 Previous work using proton acceleration to diagnose laser propagation Vulcan experiments investigated laser propagation in the relativistic transparent regime, a = 35, (5 J,!L = fs, 5!m focal spot) using proton acceleration as a diagnostic. (a).9nc 5 (b).5nc (c) 3nc (d).5nc 3 5 (e) 5nc (f) 3nc (MeV) Increasing plasma density = decreasing propagation distance => Less proton acceleration Omega EP experiment is lower intensity, a = 3, but longer pulse length,!l = ps, where hole boring through the plasma is expected to be important for the channel formation and laser propagation. (c)

4 Experimental setup Targets: Low density foam, CHO Mounted in mm x mm x 5!m washers Made by Wigen Nazarov Backlighter beam: J, ps Focus: % of energy within!m radius Peak intensity =.3 X 9 Wcm - a " 3 (a) mounted washer (b) 3 mg/cm 3 foam 5 µm (c) mg/cm 3 foam 5 µm Transmitted Scattered Light Imaging diagnostic TSLID Filtered at 53 +/- nm Proton Film Pack (PFP) Foam density (mg/cc) n e (n c ) laser Target at normal incidence

5 Preliminary results Normalized data Maximum proton energy observed = 5 MeV. normalized quantitiy.... RCF dose for MeV protons Pinhole camera signal Transmitted laser energy Angular divergence of MeV protons Foam density (mg/cc)

6 Summary and Future work Summary of data so far:! Density scan around the critical density has been shot on Omega EP! High energy proton beams were measured! Consistent trends observed with different diagnostics Future work:! Run D particle-in-cell (PIC) code for Omega EP conditions! Investigate the how much laser energy is transmitted through the foam, but shifted out of the bandwidth of the filter